from bs4 import BeautifulSoup
html_str='''
<!DOCTYPE html>
<html >
<head>
<meta charset="UTF-8">
<title>The Dormouse's story</title>
</head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" class="sister" id="link1"><!-- Elsie --></a>,
<a href="http://example.com/lacie" target="_blank" rel="external nofollow" class="sister" id="link2"><!-- Lacie --></a> and
<a href="http://example.com/tillie" target="_blank" rel="external nofollow" class="sister" id="link3">Tillie</a>; and they lived at the bottom of a well.
</p>
<p class="story">...</p>
</body>
</html>
'''
soup = BeautifulSoup(html_str,'lxml',from_encoding='utf-8')
#soup = BeautifulSoup(open('index.html')) 此方式调用需要将html_str写入到index.html文件中
print soup.prettify()
BeautifulSoup会自动选择适合的解析器解析html
beautifulsoup将复杂的html转换成树形结构，每个结点都是python对象，所有对象可以归纳为4种：如下
1）tag对象：
<title>The Dormouse's story</title>
<a href="http://example.com/elsie" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" class="sister" id="link1"><!-- Elsie --></a>
title和a标签中的内容被称为tag对象
内容该被如何获取呢？？
结合上面的代码加入
print soup.title
print soup.a
print soup.p 结果为：
<title>The Dormouse's story</title>
<a class="sister" href="http://example.com/elsie" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" target="_blank" rel="external nofollow" id="link1"><!-- Elsie --></a>
<p class="title"><b>The Dormouse's story</b></p>
获取对象名和标签名：
print soup.name
print soup.title.name 修改对象标签名：
print soup.title
soup.title.name = 'mytitle'
print soup.name
print soup.mytitle.name
print soup.mytitle
print soup.title 获取标签属性：
print soup.p['class']
print soup.p.get('class')
print soup.p.attrs 修改标签属性：
soup.p['class']='myclass'
print soup.p 结果为：
<p class="myclass"><b>The Dormouse's story</b></p>
2）NavigableString对象：
获取标签中的值
print soup.p.string BeautifuSoup使用NavigableString类包装标签中的字符串，与python中的Unicode字符串相同，骑过unicode()方法可以直接将NavigableString对象转换成Unicode字符串。
unicode_string = unicode(soup.p.string)
3）beautifulsoup对象：
beautifulsoup不是真正的html或xml的标记，没有name和attribute属性
为了标准化Tag对象，实现接口的统一，可以获取name和attribute属性
print type(soup.name)
print soup.name
print soup.attrs 结果为：
<type 'unicode'>
[document]
{}
4）Comment对象：文档注释
print soup.a.string ====> 输出：Elsie
print type(soup.a.string)===》输出：<class 'bs4.element.Comment'>
提取注释时可以根据字符串类型获取：
if type(soup.a.string)==bs4.element.Comment:
print soup.a.string
![Beautifulsoup 返回none或空字符的一种情况[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)